In our United Kingdom Patent No. GB-B-2188510 a method for TV picture motion measurement is described in which a plurality of motion vectors are derived for each of a plurality of measurement blocks of a picture and from these a list of motion vectors is derived which are applicable over the whole area of each block. The process is then repeated over the whole area of the picture. These vectors are derived using a phase correlation technique. One of these is then assigned to each elementary area of each block of the image. Other methods are also possible for generating such a list of motion vectors, for example the block matching technique described in European Patent Application No. EP-A-0395264. Each elementary area of a region of the picture to which a vector is assigned may be as small as a picture element (pixel) or it may comprise a plurality of picture elements for a block of the picture. The motion vectors thus derived may be used, for example, to generate output fields at instants in time intermediate of the time of two input fields. Such intermediate fields are required when producing slow motion effects, when transferring video images to or from film, or in standards conversion.
The methods used for deriving the motion vectors have been found to be highly satisfactory for stationary camera positions but have led to problems when a zoom of the camera is involved or a rotation of the camera about its viewing access. These problems have been particularly serious when such a zoom or rotation has been combined with a camera pan and the methods for deriving the motion vectors have in some cases broken down completely in these situations.